This invention relates to a refrigerating unit for cooling down a plurality of chambers by utilizing one refrigerating compressor, and more particularly, to a refrigerating unit suitable for use in a vending machine provided with a plurality of isolated storage chambers.
Generally, the vending machine stores different types of beverages and/or merchandise to meet the consumer's taste demands. However, these beverages and/or merchandise should be stored under predetermined temperatures to hold the flavor thereof or to maintain the freshness thereof. The predetermined temperature is determined by the characteristics of each beverage and/or merchandise item. Therefore, each chamber of the vending machine in which different type of beverages and/or merchandise are stored should be maintained at different temperatures, but the temperature in each chamber is generally maintained by operation of one refrigerating unit to reduce the cost and dead space of the vending machine.
Referring to FIG. 1, a prior art refrigerating unit for a vending machine is illustrated. The refrigerating unit 1 comprises a compressor 2, a condenser 3 and two evaporators 4a and 4b, each of which evaporators is disposed in an isolated chamber of the vending machine, respectively. The evaporators 4a and b are parallel connected with one another, and magnetic valves 5a and 5b, and capillary tubes 6a and 6b which are serially connected with one another are disposed between condenser 3 and each evaporator 4a and 4b to control the flow of refrigerant. Suction lines 7a and 7b which are connected between the suction port of compressor 2 and each evaporator 4a and 4b are closely disposed relative to capillary tubes 6a and 6b to accomplish heat exchange therebetween.
In the operation of refrigerating unit 1, the high temperature and high pressure refrigerant discharged from compressor 2 is condensed by condenser 3, and is then separated into two systems to flow in both evaporators 4a and 4b. Before flowing into evaporators 4a and 4b, the refrigerant passes through capillary tubes 6a and 6b and heat exchanged with the air passed through evaporator 4a and 4b. Thus, each isolated chamber of the vending machine in which evaporator 4a and 4b are disposed is refrigerated. Vaporized refrigerant is returned to the compressor through suction lines 7a and 7b while exchanging heat with capillary tubes 6a and 6b.
In this construction of the refrigerating unit, control of operation of either one of refrigerant circuits is accomplished by open-close operation of magnetic valve 5a and 5b even if compressor 2 is continuously driven. Therefore, one of the isolated chambers is refrigerated in the normal way and the other chamber is maintained at normal temperature. On the other hand, if two isolated chambers of a vending machine should be maintained at different temperatures in accordance with the stored merchandise, i.e., the cooling load of each chamber is different, temperature control in each chamber is generally accomplished by determination of the rate between constriction of the area of the two capillary tubes 6a and 6b. That is the amount of refrigerant flowing into each evaporator 4a and 4b can be controlled by change of the constriction area of capillary tubes 6a and 6b, and finally the chambers of the refrigerating vending machine are maintained at different temperatures, respectively.
However, the stored amount of merchandise within each isolated chamber directly changes the refrigerating load of the chamber. Therefore, if the refrigerating load in each chamber is changed, for example, the refrigerant in one of the chambers in which first evaporator 4a is disposed is increased and the refrigerating load, in the other chamber in which the second evaporator 4b is disposed, is decreased, the amount of refrigerant flowed into first evaporator 4a is insufficient and overheated refrigerant is passed through suction line 7a. Therefore, the temperature on the outer surface of suction line 7a is increased. On the other hand, the evaporation of refrigerant passing through the second evaporator 4b is insufficient, therefore, gas-liquid mixed refrigerant is passed through the suction line. Thus, the outer surface of suction line 7b is cooled down by this mixed refrigerant.
Furthermore, if the outer surface of the capillary tube is normally cooled down in a conventional way, the amount of flash gas generated within the capillary tube is reduced, to thereby reduce the flow inlet resistance of the refrigerant, and also maintain the liquid refrigerant at a lower temperature and lower pressure. On the other hand, if the temperature on the outer surface of the capillary tube is increased by external environmental factors or the capillary tube is left alone without cooling, the amount of flash gas is increased. Thus, the flow inlet resistance of refrigerant is increased, to thereby impede the smooth flow of refrigerant.
Therefore, when suction lines 7a and 7b are closely disposed relative to the evaporator of its refrigerant circuit, the temperature condition of suction lines 7a and 7b are directly influenced by the operating conditions of capillary tubes 6a and 6b. Thus, the phenomenon in each refrigerant circuit is increased, i.e., insufficient refrigerant in one circuit and over cooling in the other circuit occurs. As a result of this phenomenon, liquid refrigerant partially flows into one of the evaporators, and causes unbalanced refrigerating operation of the refrigerating unit.